In recent years, as a method for analyzing a gene function, there have been proposed various methods for regulating expression of a target gene to be analyzed.
Among those mentioned above, as a simple and powerful gene-function inhibition method, an RNA interference (RNAi) method has been widely used which uses a phenomenon in which expression of a target protein is specifically suppressed by a double-stranded RNA (dsRNA) that promotes specific decomposition of a target mRNA complementary thereto (Fire, A. et al., (1998), Nature 391, 806-811, Svobada, P. et al., (2000) Development 127, 4147-4156, Elbashir, S. M., Lendeckel, W. and Tuschl, T., (2001) Genes and Dev. 15, 188-200, Zamore, P. D. et al., (2000) Cell, 101, 25-33, Bernstein, E. et al., (2001) Nature, 409, 363-366, and the like).
In addition, so-called caged compounds each designed to regulate the activity of a target material using light have been variously developed. The caged compound is formed of a photodegradable protective group and has properties in which when it is bound to a target material, the target material is inactivated (caging), and when light is irradiated thereto, the cage is removed (uncaging), so that the original activity of the target material is restored (R. S. Givens, C. H. Park, Tetrahedron Lett., 37, 6259-6262 (1996), C. H. Park, R. S. Givens, J. Am. Chem. Soc., 119, 2453-2463 (1997), J Engels, E. J. Schlaeger, J. Med. Chem. 20, 907 (1977), J. H. Kaplan, G Forbush III, J. F. Hoffman, Biochemistry 17, 1920-1935 (1978), WO00/31588, and the like).
In biological fields, attention has been paid from early stage to the features of the cage compound, and recently, attempts have been made to regulate gene expression by using the caged compound as described above (Japanese Unexamined Patent Application Publication No. 2002-315576, Seikagaku (Biochemistry) vol. 75, No. 9, pp. 1251-1254, 2003, and the like).
This method is a method in which after an mRNA (single strand) is caged by a caged compound and is then transfected into a cell, the cell is pinpointedly irradiated with light or the like at an arbitrary timing and location, and as a result, translation of the target RNA (that is, the expression of protein) is conditionally performed.
In the above method, the expression of a target gene is suppressed by directly binding the caged compound to the single stranded mRNA; however, regulation of the expression of a target gene by suppressing the RNAi effect of an siRNA has not been reported, which is performed, for example, by crosslinking a double-stranded nucleotide, such as a double-stranded RNA (siRNA) used in the above RNAi or the like.